The effect of tannic acid on membrane enzymes and on permeability

1. 1. The effects of tannic acid on ATPases and non-specific phosphatases has been studied. 2. 2. The ATPases of a rat brain microsomal preparation showed a simple inhibition comparable with the effect found with erythrocyte cholinesterase. Tannic acid had only a small or no action on the Mg 2+−activated surface apyrase and p-nitrophenyl phosphatase activities of erythrocytes. 3. 3. The Mg 2+− and Na +−K +−Mg 2+−ATPase activities of erythrocyte ghosts, however, were markedly activated by low concentrations of tannic acid, both when this agent was applied to the ghosts directly and when applied to the erythrocytes prior to haemolysis. 4. 4. Although tannic acid is known to reduce erythrocyte anion permeability at low concentrations, it was found to have relatively little effect, either on passive cation permeability or on active efflux of 22Na. 5. 5. The possible implications of these ATPase enzyme systems in the control of ion permeability and of the disc shape of erythrocytes are discussed.